// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.
//
// THIRD PARTY LICENSE NOTICE:
//
// Portions of this code are sourced from V8:
//
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// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
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/**
 * Creates a CSV lines parser.
 */
export class CsvParser {
    /**
     * Converts \x00 and \u0000 escape sequences in the given string.
     *
     * @param input field.
     */
    escapeField(string: string) {
        let nextPos = string.indexOf("\\");
        if (nextPos === -1) return string;

        let result = string.substring(0, nextPos);
        // Escape sequences of the form \x00 and \u0000;
        let pos = 0;
        while (nextPos !== -1) {
            let escapeIdentifier = string.charAt(nextPos + 1);
            pos = nextPos + 2;
            if (escapeIdentifier === 'n') {
                result += '\n';
                nextPos = pos;
            } else if (escapeIdentifier === '\\') {
                result += '\\';
                nextPos = pos;
            } else {
                if (escapeIdentifier === 'x') {
                    // \x00 ascii range escapes consume 2 chars.
                    nextPos = pos + 2;
                } else {
                    // \u0000 unicode range escapes consume 4 chars.
                    nextPos = pos + 4;
                }
                // Convert the selected escape sequence to a single character.
                let escapeChars = string.substring(pos, nextPos);
                if (escapeChars === '2C') {
                    result += ',';
                } else {
                    result += String.fromCharCode(parseInt(escapeChars, 16));
                }
            }

            // Continue looking for the next escape sequence.
            pos = nextPos;
            nextPos = string.indexOf("\\", pos);
            // If there are no more escape sequences consume the rest of the string.
            if (nextPos === -1) {
                result += string.substr(pos);
            } else if (pos !== nextPos) {
                result += string.substring(pos, nextPos);
            }
        }
        return result;
    }

    /**
     * Parses a line of CSV-encoded values. Returns an array of fields.
     *
     * @param line Input line.
     */
    parseLine(line: string) {
        var pos = 0;
        var endPos = line.length;
        var fields: string[] = [];
        if (endPos == 0) return fields;
        let nextPos = 0;
        while (nextPos !== -1) {
            nextPos = line.indexOf(',', pos);
            let field;
            if (nextPos === -1) {
                field = line.substr(pos);
            } else {
                field = line.substring(pos, nextPos);
            }
            fields.push(this.escapeField(field));
            pos = nextPos + 1;
        };
        return fields
    }
}
